Zoom lens and image projection apparatus having the same

ABSTRACT

A zoom lens comprises a plurality of lens units including a first lens unit disposed most adjacent to an enlargement side and having negative refractive power, wherein one or more lens units of the plurality of lens units are moved in the direction of the optical axis thereof during magnification change, and wherein the first lens unit includes a 1-1st lens unit comprising at least one lens of negative refractive power and moved during focusing and a 1-2nd lens unit having positive refractive power, and fixed during focusing.

This application is a continuation of application Ser. No. 11/619,852,filed Jan. 4, 2007, which is a continuation of application Ser. No.11/360,232, filed Feb. 22, 2006, now U.S. Pat. No. 7,190,528, issuedMar. 13, 2007, both of which are incorporated by reference in theirentirety. This application also claims priority from Japanese PatentApplication No. 2005-045456 filed Feb. 22, 2005, which is herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a zoom lens and an image projection apparatushaving the same, and is suitable for a liquid crystal projector having,for example, a long back focal length, and having high opticalperformance at various projection magnifications.

2. Related Background Art

There have heretofore been proposed various liquid crystal projectors(image projection apparatuses) using a display element such as a liquidcrystal display element to project an image formed on the displayelement onto a screen surface.

Characteristics mentioned below are required of a projection lens foruse in these liquid crystal projectors.

In color liquid crystal projection of a three-element type using threeliquid crystal display elements, generally, light from a white lightsource is separated into red, green and blue colors by a colorseparating optical system, and these color lights are directed to therespective liquid crystal display elements, and the lights emerging fromthose liquid crystal display elements are combined by a color combiningoptical system and are made to be incident on a projection lens.

In that projection, the projection lens must have a back focal length ofa certain constant length so as to provide a space between each liquidcrystal display element and the projection lens for disposing therein aprism or the like for combining the color lights after transmittedthrough the liquid crystal display elements.

If the angles of the light beams incident from the liquid crystaldisplay elements onto the color combining optical systems change, thespectral transmittance of the color combining optical system changes inconformity therewith, and the brightness of each color in the projectedimage is changed depending on the angle of view and the image becomes animage difficult to see. Therefore, in order to lessen the influence ofthe dependence on the angle, the color combining optical system must bea so-called telecentric optical system of which the pupil on the liquidcrystal display element (reduction conjugate surface) side issubstantially at infinity.

When the pictures (images) of the liquid crystal display elements of thethree colors are combined and projected onto a screen, pixels of therespective colors must be superposed one upon another on the entire areaof the screen so that high resolution feeling may not be spoiled by, forexample, doubly displaying characters or the like.

Therefore, color misregistration (chromatic aberration of magnification)occurring in the projection lens must be well corrected in a visiblelight zone.

Distortion must be well corrected so that the projected image may not bedistorted and difficult to see.

The projection lens must be a bright projection lens of small Fno (Fnumber) so as to be capable of efficiently introducing the light fromthe light source.

The projector carrying a compact liquid crystal panel thereon must becompact and light in weight to attach importance to portability andmobility.

A good projected image must be obtained at various projection distances,that is, the aberration fluctuation during focusing must be small.

As a zoom lens adapted to satisfy these requirements, there has been azoom lens for a projector of which the focusing is effected with onlysome of optical elements in lens units moved (Japanese PatentApplication Laid-open No. H10-186235, U.S. Pat. No. 6,580,564 andJapanese Patent Application Laid-open No. 2004-226803).

Japanese Patent Application Laid-open No. H10-186235 discloses afive-unit zoom lens comprising, in succession from a screen side, lensunits of negative, positive, positive, negative and positive refractivepower and in which the rearmost (projected image side) positive lens ina first lens unit comprising four positive, negative, negative andpositive lenses is fixed and three lenses on the screen side are movedto thereby effect focusing.

U.S. Pat. No. 6,580,564 and Japanese Patent Application Laid-open No.2004-226803 disclose a five-unit zoom lens comprising, in successionfrom a screen side, lens units of negative, positive, positive, negativeand positive refractive power and in which a first lens unit is composedof two lens elements having negative refractive power, and the intervalbetween these lens elements is changed to thereby effect focusing. Bothof these are such that a positive lens is included in a focusing elementand weakens the refractive power of the entire focusing element.

Also, as a projection lens for a liquid crystal projector, there isproposed a six-unit zoom lens comprising, in succession from anenlargement conjugate side (this term is interchangeably used herein inthe same meaning as a front side and an enlarging side), six lens unitsas a whole by the arrangement of first to sixth lens units of negative,positive, positive, negative, positive (or negative) and positiverefractive power, and in which a predetermined lens unit of them isappropriately moved to thereby effect zooming (U.S. Publication No.US-2001-050818).

In this six-unit zoom lens, during zooming from a wide angle end to atelephoto end, in order that with the first and sixth lens units asbeing fixed, the second to fifth lens units therebetween may all bemoved to a reduction conjugate side (this term is interchangeably usedherein in the same meaning as a rear side and a reduction side), thefull length of the lens is kept constant during zooming. Also, this zoomlens is a zoom lens in which distortion and chromatic aberration duringzooming are lessened and which is telecentric on the reduction conjugateside. In the configuration disclosed in this U.S. Publication No.US-2001-050818, there is disclosed that the first lens unit is composedof three positive, negative and negative lenses from the enlargementconjugate side, and this first lens unit is driven to thereby effectfocus adjustment.

Generally, as a method of suppressing the fluctuations of variousaberrations when focusing is effected, there is a method ofstrengthening the refractive power of a focusing lens unit as far aspossible, and lessening the movement amount of the focusing lens to theutmost. In the aforementioned Japanese Patent Application Laid-open No.H10-186235, U.S. Pat. No. 6,580,564 and Japanese Patent ApplicationLaid-open No. 2004-226803, in the lens construction in the first lensunit, the focusing lens unit is not composed of only negative lenses andtherefore, there has been the tendency that the refractive power of thefocusing lens unit becomes weak, and the movement amount thereof duringfocusing becomes great and the fluctuations of various aberrationsbecome great.

Further, it is often the case with the lens construction of a zoom lensused in a projector that it is made into a retrofocus type in order toobtain a long back focal length, and lens units having strong positiverefractive power are disposed on a reduction side in order to make thereduction side telecentric.

The zoom lens of such a construction, however, has the tendency that theasymmetry of the entire lens system increases for example, as chromaticaberration of magnification in blue occurs more under (direction of anoptical axis) than that in green.

Also, the smaller becomes the number of lenses, the more increases therefractive power of each lens and therefore, particularly a negativelens located more adjacent to the reduction side than a stop becomesliable to cause chromatic aberration of magnification of a high order inthe over direction. Also, the greater becomes the zoom ratio, thegreater the fluctuation of chromatic aberration of magnification fromthe wide angle end to the telephoto end also tends to become.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a zoom lens suitablefor use, for example, in a liquid crystal projector which achieves thedownsizing of an entire lens system, and yet well corrects variousaberrations resulting from focusing, and has good optical performanceover the whole of a projection distance.

It is another object of the present invention to provide a zoom lenssuitable for use in a projector which corrects chromatic aberration ofmagnification well and can easily obtain high optical performance.

The zoom lens of the present invention comprises:

a plurality of lens units including a first lens unit disposed mostadjacent to an enlargement side and having negative refractive power;

at least one of the plurality of lens units being moved in the directionof the optical axis thereof during a magnification change;

said first lens unit including:

a 1-1st lens unit comprising at least one lens having negativerefractive power, and moved during focusing; and

a 1-2nd lens unit having positive refractive power, and fixed duringfocusing.

The zoom lens of the present invention comprises:

a first lens unit disposed most adjacent to an enlargement side, andhaving negative refractive power;

a last lens unit disposed most adjacent to a reduction side, and havingpositive refractive power; and

one or more lens units moved in the direction of the optical axisthereof during zooming (magnification change);

wherein the following condition is satisfied,

32<νdR−νdF

where νdF is the Abbe number of the material of which a first lens inthe first lens unit disposed most adjacent to the enlargement side hasnegative refractive power is made, and νdR the Abbe number of thematerial of which the last lens in said last lens unit which is disposedmost adjacent to the reduction side has positive refractive power ismade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the essential portions of an imageprojection apparatus using a zoom lens according to Embodiment 1.

FIG. 2 shows aberrations at the wide angle end of a zoom lens accordingto Numerical Embodiment 1.

FIG. 3 shows aberrations at the telephoto end of the zoom lens accordingto Numerical Embodiment 1.

FIGS. 4A and 4B show the chromatic aberration of magnification of thezoom lens according to Numerical Embodiment 1.

FIG. 5 is a schematic view of the essential portions of an imageprojection apparatus using a zoom lens according to Embodiment 2.

FIG. 6 shows aberrations at the wide angle end of a zoom lens accordingto Numerical Embodiment 2.

FIG. 7 shows aberrations at the telephoto end of the zoom lens accordingto Numerical Embodiment 2.

FIG. 8 is a schematic view of the essential portions of an imageprojection apparatus using a zoom lens according to Embodiment 3.

FIG. 9 shows aberrations at the wide angle end of a zoom lens accordingto Numerical Embodiment 3.

FIG. 10 shows aberrations at the telephoto end of the zoom lensaccording to Numerical Embodiment 3.

FIG. 11 is an illustration of the optical system of a projection typeimage display apparatus according to the present embodiment.

FIG. 12 is a schematic view of the essential portions of a color liquidcrystal projector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention can be described as follows.

A zoom lens according to the embodiment is provided with a plurality oflens units including a lens unit GF disposed on the foremost side(magnifying side) and having negative refractive power (optical power),and one or more other lens units of the plurality of lens units than thelens unit GF are moved in the direction of the optical axis thereof tothereby effect zooming, and project image information disposed on arearward side (reduction side) onto a predetermined surface. At thistime, the lens unit GF is characterized by comprising a lens unit Ahaving negative refractive power moved during focusing and a lens unit Bhaving positive refractive power immovable during focusing. Herein, alens unit not only means a plurality of lenses, but even a single lensis also referred to as a lens unit.

At this time, the lens unit A is composed of only a lens of negativerefractive power.

Thus, during focusing, only lenses having negative refractive power inthe first lens unit are moved to thereby heighten the refractive powerof a focusing element, and decrease the movement amount of a focusinglens unit, and minimize the fluctuations of various aberrations, therebylessening a change in optical performance due to the difference inprojection distance.

A zoom lens according to another embodiment is provided with a pluralityof lens units including a lens unit GF disposed on the foremost side andhaving negative refractive power (optical power), and a lens unit GRdisposed on the rearmost side and having positive refractive power(optical power), and one or more other lens units of the plurality oflens units than the lens unit GF and the lens unit GR are moved in thedirection of the optical axis thereof to thereby effect zooming, andproject image information disposed on a rearward side onto apredetermined surface. At this time, a lens GFa on the foremost side ofthe lens unit GF has negative refractive power, and a lens GRb on therearmost side of the lens unit GR has positive refractive power, andthis zoom lens is characterized by satisfying the condition that

32<νdR−νdF.   (1)

where νdF and νdR represent the Abbe numbers of the materials of whichthe lens GFa and the lens GRb are made, respectively.

Also, under such a construction, the lens system GF is characterized bybeing constituted, in succession from the front side to the rear side,by a lens unit A having negative refractive power moved during focusing,and a lens unit B of positive refractive power fixed during focusing.

Further, the lens unit A is composed of only lenses having negativerefractive power.

As described above, the lens GFa and the lens GRb are constructed sothat the Abbe numbers of the materials thereof may satisfy theconditional expression (1), whereby chromatic aberration ofmagnification is corrected well.

Particularly by satisfying the conditional expression (1), even in azoom lens of a great zoom ratio, the fluctuation of chromatic aberrationof magnification is preferably corrected by a small number of lenses.

High dispersion glass is used as the material of the lens GFa on theforemost side, and low dispersion glass is used as the material of thelens GRb on the rearmost side. In the lens GFa on the foremost side, achange in the incidence height of a ray of light at a great image heightbecomes great from the wide angle end to the telephoto end andtherefore, chromatic aberration of magnification of a high orderoccurring under is generated greatly at the wide angle end and small atthe telephoto end. At this time, the conditional expression (1) issatisfied, whereby chromatic aberration of magnification of a high orderin the under direction can be generated so as to negate chromaticaberration of magnification of a high order in the over direction inconformity with zooming, and suitable chromatic aberration ofmagnification is corrected by a small number of constituent lenses.

At this time, it is preferable to set the upper limit value of theconditional expression (1) so as to satisfy the condition that

νdR−νdF<50.   (1a)

According to this, it becomes easy to correct chromatic aberration ofmagnification better over the whole of the projection distance.

Also, in order to make the rear side telecentric, it is preferable tosatisfy the condition that

7.0<|DP/fw|  (2),

where DP represents the distance from a position at which imageinformation on the rear side (reduction side conjugate position) isdisposed to an exit pupil, and fw represents the focal length of theentire system at the wide angle end. It is more preferable that thevalue of the conditional expression (2) be greater than 10.0. Also, itis desirable that |DP/fw| be 100 or less, and preferably less than 20.

If the conditional expression (2) is not satisfied, telecentricitybecomes bad, the brightness of each color becomes different depending onan angle of view when the present invention is applied to a colorprojector, and this is not good.

In each embodiment, each element is constructed as described above, tothereby realize a zoom lens suitable for use in a projector which issmall in the fluctuations in aberrations due to focusing, and is smallin the fluctuation in chromatic aberration of magnification duringzooming.

Also, an image projection apparatus according to the present embodimenthas any one of the aforementioned zoom lenses, and a display unit forforming an original image, and projects the original image formed by thedisplay unit onto a screen surface (a projection surface, and of course,in the case of a rear projection type, desirably an image plane or ascreen surface having a lenticular lens or the like and having theaction of diffusing incident light) by the aforementioned zoom lens.

The drawings referred to in the present embodiment will now be brieflydescribed.

FIG. 1 is a schematic view of the essential portions of an imageprojection apparatus (liquid crystal video projector) using a zoom lensaccording to Embodiment 1. FIGS. 2 and 3 show aberrations at the wideangle end (short focal length side) and the telephoto end (long focallength side), respectively, in a case of an object distance (thedistance from the first lens unit) being 1.7 m when the numerical valuesof Numerical Embodiment 1 to be described later corresponding toEmbodiment 1 of the present invention are represented by the unit of mm.

FIGS. 4A and 4B show chromatic aberrations of magnification of awavelength 610 nm (red) and a wavelength 470 nm (blue) relative to thewavelength 550 nm of Numerical Embodiment 1, at the wide angle end andthe telephoto end, respectively, at each image height Y when the objectdistance is 1.7 m.

FIG. 5 is a schematic view of the essential portions of an imageprojection apparatus using a zoom lens according to Embodiment 2 of thepresent invention. FIGS. 6 and 7 show aberrations at the wide angle endand the telephoto end, respectively, in a case of the object distancebeing 1.7 m when the numerical values of Numerical Embodiment 2 to bedescribed later corresponding to Embodiment 2 of the present inventionare represented by the unit of mm.

FIG. 8 is a schematic view of the essential portions of an imageprojection apparatus using a zoom lens according to Embodiment 3 of thepresent invention. FIGS. 9 and 10 show aberrations at the wide angle endand the telephoto end, respectively, in a case of the object distancebeing 1.7 m when the numerical values of Numerical Embodiment to bedescribed later corresponding to Embodiment 3 of the present inventionare represented by the unit of mm.

FIGS. 1, 5 and 8 show the image projection apparatuses according toembodiments 1 to 3 in which the original image (projected image) on anLCD is enlarged and projected onto a screen surface S by the use of thezoom lens (projection lens) PL.

The letter S designates a screen surface (projection surface), and LCDdenotes the original image (projected image) of a liquid crystal panel(liquid crystal display element) or the like. The screen surface S andthe original image LCD are in a conjugate relation with each other, andgenerally the screen surface S corresponds to the enlargement side(forward) at a conjugate point at a longer distance (first conjugatepoint), and the original image LCD corresponds to the reduction side(rearward) at a conjugate point at a shorter distance (second conjugatepoint). When the zoom lens is used as a photographing system, the screensurface S side corresponds to the object side, and the original imageLCD side corresponds to the image side.

GB designates a glass block (prism) provided in optical designcorrespondingly to a color combining prism or a polarizing filter and acolor filter or the like.

The zoom lens PL is mounted on a liquid crystal video projector mainbody (not shown) through a connecting member (not shown). The liquidcrystal display element LCD side subsequent to the glass block GB isincluded in the projector main body.

The zoom lenses according to Embodiments 1 to 3 have F number 1.75, andproject the image information onto a 100 inch type screen surface at ashort projection distance of 2.5 m (when the numerical embodiments arerepresented by the unit of mm).

In the aberration graphs of FIGS. 2, 3, 6, 7, 8 and 9, G indicates anaberration at a wavelength 550 nm, and both of S (the inclination of asagittal image plane) and M (the inclination of a meridional imageplane) indicate aberrations at a wavelength 550 nm. Fno is F number. Wis a half angle of view, and Y is an image height (image height on theprojected side).

Description will now be made of the details of the zoom lens accordingto each embodiment.

In Embodiment 1 of FIG. 1, L1 designates a first lens unit havingnegative refractive power, L2 denotes a second lens unit having positiverefractive power, L3 designates a third lens unit having positiverefractive power, L4 denotes a fourth lens unit having negativerefractive power, L5 designates a fifth lens unit having positiverefractive power, and L6 denotes a sixth lens unit having positiverefractive power.

The first lens unit L1 has a 1A-th lens unit L1A having negativerefractive power, and a 1B-th lens unit L1B having positive refractivepower.

In Embodiment 1, during zooming (magnification) from the wide angle endto the telephoto end, the second lens unit L2, the third lens unit L3,the fourth lens unit L4 and the fifth lens unit L5 are independentlymoved to a first conjugate point side (the screen S side) which is theenlargement side as indicated by arrows.

The first lens unit L1 and the sixth lens unit L6 are not moved forzooming. The 1A-th lens unit L1A having negative refractive power in thefirst lens unit L1 is moved on the optical axis thereof to therebyeffect focusing. The 1B-th lens unit L1B is immovable for focusing.

An aperture stop SP is provided between the third lens unit L3 and thefourth lens unit L4, and is moved with the third lens unit L3 duringzooming. A multi-layer coat for preventing reflection is provided oneach lens surface.

In Embodiment 1, in succession from the object side to the image side,the 1A-th lens unit L1A comprises a negative lens G11, a negative lensG12 of which the two lens surfaces are of an aspherical shape, and anegative lens G13, and the 1B-th lens unit L1B comprises a positive lensG14 of which the rear surface is of a convex shape. Here, the 1A-th lensunit is composed of three negative lenses, but of course may be composedof a negative lens, or may be composed of two, four or more negativelenses. That is, the 1A-th lens unit L1A can be composed of onlynegative lenses. However, from the viewpoints of the suppression of theaberrations of the entire system and the downsizing of the entiresystem, it may be composed of two or more and five or less negativelenses, and preferably of three or more negative lenses. Also, the 1B-thlens unit may be composed of two positive lenses. Also, a lens (opticalelement) having substantially no refractive power (having no opticalpower) may be disposed more adjacent to the enlargement conjugate sidethan the 1A-th lens unit L1A. It is desirable that the focal length ofthis lens disposed more adjacent to the enlargement conjugate side thanthe 1A-th lens unit L1A be 20 times (preferably 100 times) as great asthe focal length of the zoom lens at the wide end thereof or greater.

The second lens unit L2 comprises a positive lens G21 of which the frontsurface is of a convex shape.

The third lens unit L3 comprises a cemented lens comprising a positivelens G31 and a negative lens G32.

The fourth lens unit L4 comprises a negative lens G41 of which the twolens surfaces are of a concave shape.

The fifth lens unit L5 comprises a positive lens G51 of which the twolens surfaces are of a convex shape, and a positive lens G52 of whichthe rear surface is of a convex shape.

The two lens surfaces of the positive lens G52 are of an asphericalshape.

The sixth lens unit L6 comprises a positive lens G61 of which the twolens surfaces are of a convex shape.

In Embodiment 1, design is made such that during focusing, only the lenselements having negative refractive power in the first lens unit L1 aremoved. Thereby, the refractive power (negative) of the moved elementsduring focusing becomes greater than that of the entire first lens unitL1, and the movement amount can be more decreased than that in a casewhere focusing is effected by the entire first lens unit L1 and inaccordance therewith, the fluctuations of aberrations are decreased.Also, the three negative lenses G11 to G13 constituting the movedelements during focusing are collectively moved to the enlargement sideand therefore, the construction of a lens barrel can be realized easily.

In Embodiment 2 shown in FIG. 5, L1 designates a first lens unit havingnegative refractive power, L2 denotes a second lens unit having positiverefractive power, L3 designates a third lens unit having positiverefractive power, L4 denotes a fourth lens unit having negativerefractive power, L5 designates a fifth lens unit having positiverefractive power, L6 denotes a sixth lens unit having positiverefractive power, and L7 designates a seventh lens unit having positiverefractive power.

The first lens unit L1 has a 1A-th lens unit L1A having negativerefractive power, and a 1B-th lens unit L1B having positive refractivepower.

In Embodiment 2, during zooming (magnification) from the wide angle endto the telephoto end, the second lens unit L2, the third lens unit L3,the fourth lens unit L4, the fifth lens unit L5 and the sixth lens unitL6 are independently moved to the first conjugate point side (the screenS side) which is the enlargement side, as indicated by arrows. Here, thefirst lens unit L1 may also be moved during zooming. This also holdstrue of the other embodiments.

The first lens unit L1 and the seventh lens unit L7 are not moved forzooming. The 1A-th lens unit L1A having negative refractive power in thefirst lens unit L1 is moved on the optical axis thereof to therebyeffect focusing. The 1B-th lens unit L1B is immovable for focusing.

An aperture stop SP is provided between the third lens unit L3 and thefourth lens unit L4, and is moved with the third lens unit L3 duringzooming. A multi-layer coat for preventing reflection is provided oneach lens surface.

In Embodiment 2, in succession from the object side to the image side,the 1A-th lens unit L1A comprises a negative lens G11, a negative lensG12 of which the two lens surfaces are of an aspherical shape, and anegative lens G13, and the 1B-th lens unit L1B comprises a positive lensG14 of which the rear surface is of a convex shape. Here, the 1Ath lensunit composed of three negative lenses, but of course, may be compriseda negative lens, or may be composed of two, four or more negativelenses. That is, the 1A-th lens unit L1A can be composed of onlynegative lenses. However, from the viewpoints of the suppression of theaberrations of the entire system and the downsizing of the entiresystem, it is preferable that the 1A-th lens unit L1A be composed of twoor more and five or less negative lenses, or preferably of three or morenegative lenses. The 1B-th lens unit may also be composed of twopositive lenses. Also, a lens (optical element) having substantially norefractive power (having no optical power) may be disposed more adjacentto the enlargement conjugate side than the 1A-th lens unit L1A. It isdesirable that the focal length of this lens disposed more adjacent tothe enlargement conjugate side than the 1A-th lens unit L1A be 20 times(preferably 100 times) as great as the focal length of the zoom lens atthe wide end thereof or greater.

The second lens unit L2 comprises a positive lens G21 of which the frontsurface is of a convex surface. The third lens unit L3 comprises acemented lens comprising a positive lens G31 and a negative lens G32.The fourth lens L4 comprises a negative lens G41 of which the two lenssurfaces are of a concave shape. The fifth lens unit L5 comprises apositive lens G51 of which the two lens surfaces are of a convex shape.The sixth lens unit L6 comprises a positive lens G61 of which the rearsurface is of a convex shape.

The two lens surfaces of the positive lens G61 are of an asphericalshape.

The seventh lens unit L7 comprises a positive lens G71 of which the twolens surfaces are of a convex shape.

In Embodiment 2, the zoom lens as a whole is composed of seven lensunits, and the fluctuations of aberrations are made small with zooming.The optical action when focusing is effected by the 1A-th lens unit L1Ais the same as that in Embodiment 1.

In Embodiment 3 shown in FIG. 8, L1 designates a first lens unit havingnegative refractive power, L2 denotes a second lens unit having positiverefractive power, L3 designates a third lens unit having positiverefractive power, L4 denotes a fourth lens unit having positiverefractive power, and L5 designates a fifth lens unit having positiverefractive power. The first lens unit L1 has a 1A-th lens unit L1Ahaving negative refractive power and a 1B-th lens unit L1B havingpositive refractive power.

In Embodiment 3, during zooming (magnification) from the wide angle endto the telephoto end, the second lens unit L2, the third lens unit L3and the fourth lens unit L4 are independently moved to the firstconjugate point side (the screen S side) which is the enlargement side,as indicated by arrows.

The first lens unit L1 and the fifth lens unit L5 are not moved forzooming. The 1A-th lens unit L1A having negative refractive power in thefirst lens unit L1 is moved on the optical axis thereof to therebyeffect focusing. The 1B-th lens unit L1B is immovable for focusing.

An aperture stop SP is provided between the third lens unit L3 and thefourth lens unit L4, and is moved with the third lens unit L3 duringzooming. A multi-layer coat for preventing reflection is provided oneach lens surface.

In Embodiment 3, in succession from the object side to the image side,the 1A-th lens unit L1A comprises a negative lens G11, a negative lensG12 of which the two lens surfaces are of an aspherical shape, and anegative lens G13, and the 1B-th lens unit L1B comprises a positive lensG14 of which the rear surface is of a convex shape. Here, the 1A-th lensunit is composed of three negative lenses, but of course, may becomposed of a negative lens, or may be composed of two, four or morenegative lenses. That is, the 1A-th lens unit can be composed of onlynegative lenses. However, from the viewpoints of the suppression of theaberrations of the entire system and the downsizing of the entiresystem, it is preferable that the 1A-th lens unit L1A be composed of twoor more and five or less negative lenses, and preferably of three ormore negative lenses. The 1B-th lens unit may also be composed of twopositive lenses. Also, a lens (optical element) having substantially norefractive power (having no optical power) may be disposed more adjacentto the enlargement conjugate point side than the 1A-th lens unit L1A. Itis desirable that the focal length of this lens disposed more adjacentto the enlargement conjugate point side than the 1A-th lens unit L1A be20 times (preferably 100 times) as great as the focal length of the zoomlens at the wide end thereof or greater.

The second lens unit L2 comprises a positive lens of which the frontsurface is of a convex shape. The third lens unit L3 comprises acemented lens comprising a positive lens G31 and a negative lens G32.The fourth lens unit L4 comprises a negative lens G41 of which the twolens surfaces are of a concave shape, a positive lens G42 of which thetwo lens surfaces are of a convex shape, and a positive lens G43 ofwhich the rear surface is of a convex shape.

The two lens surfaces of the positive lens G43 are of an asphericalshape.

The fifth lens unit L5 comprises a positive lens G51 of which the twolens surfaces are of a convex shape.

In Embodiment 3, the zoom lens as a whole is composed of five lensunits, and the mutual mounting error of the negative lens G41 andpositive lens G42 which are relatively high in degree of eccentricitydeviance is decreased. Thereby the manufacture of the zoom lens is madeeasy. The optical action when focusing is effected by the 1A-th lensunit L1A is the same as that in Embodiment 1.

Reference is now had to FIG. 11 to describe a projection type imagedisplay apparatus using any one of the zoom lenses described above inEmbodiments 1 to 3 as a projection lens (projection optical system).Here, the optical construction of a projection type image displayapparatus carrying thereon a reflection type liquid crystal displayelement (use may be made of an image forming element such as areflection type liquid crystal panel or of course, a projection typeliquid crystal panel) composed of a lamp 1, an illuminating opticalsystem a, a color separating and combining optical system β and aprojection lens optical system 70 (see FIG. 1) in a projection lensbarrel 5 will be described with reference to FIG. 11.

In FIG. 11, the reference numeral 41 designates a light emitting tubeemitting white light with continuous spectrum, and the reference numeral42 denotes a reflector for condensing the light from the light emittingtube 41 in a predetermined direction, and the light emitting tube 41 andthe reflector 42 together form an element of the lamp 1.

The reference character 43 a denotes a first cylinder array composed ofa lens array in which a plurality of cylindrical lenses havingrefractive power in a vertical direction (a direction perpendicular tothe plane of the drawing sheet of FIG. 11) in the direction of travel ofthe light from the lamp 1, the reference character 43 b designates asecond cylinder array composed of a lens array comprising cylindricallenses corresponding to the individual cylindrical lenses of the firstcylinder array 43 a, the reference numeral 44 denotes an ultraviolet rayabsorbing filter, and the reference numeral 45 designates a polarizedlight converting element for properly arranging non-polarized light intopredetermined polarized light and emitting it.

The reference numeral 46 denotes a front compressor composed of acylindrical lens having refractive power in a horizontal direction (inthe plane of the drawing sheet of FIG. 11), the reference numeral 47designates a mirror for changing the optical axis by 90 degrees, thereference numeral 48 denotes a condenser lens, and the reference numeral49 designates a rear compressor composed of a cylindrical lens havingrefractive power in the horizontal direction.

Each element described above constitutes an element of the illuminatingoptical system α.

The reference numeral 58 denotes a dichroic mirror for reflecting lightsof blue (B) and red (R) wavelength ranges, and transmitting light ofgreen (G) wavelength range therethrough. The reference numeral 59designates an incidence side polarizing plate comprising a transparentsubstrate and a polarizing element stuck thereon, and it transmits onlyS-polarized light therethrough. The reference numeral 60 denotes a firstpolarized beam splitter for transmitting P-polarized light therethroughand reflecting the S-polarized light, and having a polarized lightseparating surface 60 a.

The reference characters 61R, 61G and 61B designate a reflection typeliquid crystal display element (TN type liquid crystal and other liquidcrystal display elements are the same as this) for red (R) forreflecting incident light and modulating an image, a reflection typeliquid crystal display element for green (G), and a reflection typeliquid crystal display element for blue (B), respectively.

The reference characters 62R, 62G and 62B denote a quarter wavelengthplate for red, a quarter wavelength plate for green and a quarterwavelength plate for blue, respectively. The reference numeral 64designates an incidence side polarizing plate for R and B comprising atransparent substrate and a polarizing element stuck thereon, and ittransmits only the S-polarized light therethrough. The reference numeral65 denotes a first color selective phase difference plate which changesthe polarization direction of the light B by 90 degrees, and does notchange the polarization direction of the light R. The reference numeral66 designates a second polarized beam splitter for transmitting theP-polarized light therethrough, and reflecting the S-polarized light,and having a polarized light separating surface 66 a.

The reference numeral 67 denotes a second color selective phasedifference plate which changes the polarization direction of the light Rby 90 degrees, and does not change the polarization direction of thelight B.

The reference numeral 68 designates an emergence side polarizing plate(polarizing element) for R and B, which transmits only the S-polarizedlight. The reference numeral 69 denotes a third polarized beam splitter(color combining means) for transmitting the P-polarized lighttherethrough, and reflecting the S-polarized light, and having apolarized light separating surface 69 a.

Each of the members from the dichroic mirror 58 to the third polarizedbeam splitter 69 constitutes an element of the color separating andcombining optical system β.

The reference numeral 70 designates a projection lens optical system. Animage display optical system is constituted by the illuminating opticalsystem α, the color separating and combining optical system 13 and theprojection lens optical system 70.

Optical action will now be described.

The light emitted from the light emitting tube 41 is condensed in apredetermined direction by the reflector 42. The reflecting surface ofthe reflector 42 has a parabolic surface shape, and the light from theparabolic surface becomes a light beam parallel to the symmetry axis(optical axis) of the parabolic surface. However, the light beam fromthe light emitting tube 41 is not a light beam from an ideal point lightsource, but the light emitting tube 41 has a light emitting portion of afinite size and therefore, the light beam to be condensed also includesmuch of a component of light which is not parallel to the symmetry axisof the parabolic surface.

These light beams are incident on the first cylinder array 43 a. Thelight beams incident on the first cylinder array 43 a are divided into aplurality of light beams conforming to the respective cylinder lensesand are condensed (a plurality of light beams band-shaped in thehorizontal direction), and form a plurality of light beams (a pluralityof light beams band-shaped in the horizontal direction) near thepolarized light converting element 45 through the ultraviolet rayabsorbing filter 44 and via the second cylinder array 43 b.

The polarized light converting element 45 comprises a plurality ofpolarized light separating surfaces arranged in a vertical direction, areflecting surface and a half wavelength plate, and the plurality oflight beams are incident on the polarized light separating surfacescorresponding to the row thereof, and are divided into light of atransmitted P-polarized component and light of a reflected S-polarizedcomponent.

The light of the reflected S-polarized component is reflected by thereflecting surface, and emerges in the same direction as the P-polarizedcomponent. On the other hand, the light of the transmitted P-polarizedcomponent is transmitted through the half wavelength plate and isconverted into the same polarized component as the S-polarizedcomponent, and emerges as light having had its polarization directionregularized. The plurality of polarization-converted light beams (theplurality of light beams band-shaped in the horizontal direction) arereflected by 90 degrees by the reflecting mirror 47 through the frontcompressor 46 after they have emerged from the polarized lightconverting element 45, and come to the condenser lens 48 and the rearcompressor 49.

Here, the optical action of the front compressor 46, the condenser lens48 and the rear compressor 49 is set appropriately. The plurality oflight beams assume a shape in which rectangular images overlap oneanother, and form a rectangular uniform illuminating area.

Reflection type liquid crystal display elements 61R, 61G and 61G whichwill be described later are disposed in this illuminating area. Next,the light made into the S-polarized light by the polarized lightconverting element 45 is incident on the dichroic mirror 58. Thedichroic mirror 58 reflects light B (wavelength 430 to 495 nm) and lightR (wavelength 590 to 650 nm) and transmits light G (wavelength 505 to580 nm) therethrough.

The optical path of the light G will now be described.

The light G transmitted through the dichroic mirror 58 is incident onthe incidence side polarizing plate 59. The light G is the S-polarizedlight still after separated by the dichroic mirror 58. The light G,after it has emerged from the incidence side polarizing plate 59, isincident on the first polarized beam splitter 60 as the S-polarizedlight and is reflected by the polarized light separating surface, andcomes to the reflection type liquid crystal display element 61G for G.In the reflection type liquid crystal display element 61G for G, thelight G is image-modulated and reflected. Of the reflected light Gimage-modulated, an S-polarized component is again reflected by thepolarized light separating surface 60 a of the first polarized beamsplitter 60, is returned to the light source 1 side and is removed fromthe projected light.

On the other hand, of the reflected light of the image-modulated lightG, a P-polarized component is transmitted through the polarized lightseparating surface 60 a of the first polarized beam splitter 60, andtravels toward the third polarized beam splitter 69 as the projectedlight.

At this time, in a state in which all the polarized components have beenconverted into the S-polarized light (a state in which black isdisplayed), the slow axis of the quarter wavelength plate 62G providedbetween the first polarized beam splitter 60 and the reflection typeliquid crystal display element 61G for the light G is adjusted to apredetermined direction, whereby the influence of the disturbance of thepolarized state occurring in the first polarized beam splitter 60 andthe reflection type liquid crystal display element 61G for G can besuppressed to a small level.

The light G having emerged from the first polarized beam splitter 60 isincident on the third polarized beam splitter 69 as P-polarized light,is transmitted through the polarized light separating surface 69 a ofthe third polarized beam splitter 69 and comes to the projection lens70.

On the other hand, the light R and the light B reflected by the dichroicmirror 58 are incident on the incidence side polarizing plate 64. Thelight R and the light B are S-polarized light still after separated bythe dichroic mirror 58. Then, the light R and the light B emerge fromthe incidence side polarizing plate 64, and thereafter are incident onthe first color selective phase difference plate 65. The first colorselective phase difference plate 65 has the action of rotating thepolarization direction of only the light B by 90 degrees, whereby thelight B and the light R are incident on the second polarized beamsplitter 66 as P-polarized light and S-polarized light, respectively.The light R incident on the second polarized beam splitter 66 as theS-polarized light is reflected by the polarized light separating surfaceof the second polarized beam splitter 66, and comes to the reflectiontype liquid crystal display element 61R for the light R. Also, the lightB incident on the second polarized beam splitter 66 as the P-polarizedlight is transmitted through the polarized light separating surface 66 aof the second polarized beam splitter 66 and comes to the reflectiontype liquid crystal display element 61B for the light B.

The light R incident on the reflection type liquid crystal displayelement 61R for the light R is image-modulated and reflected. Of thereflected light of the image-modulated light R, the S-polarizedcomponent is again reflected by the polarized light separating surface66 a of the second polarized beam splitter 66 and is returned to thelight source 1 side, and is removed from the projected light. On theother hand, of the reflected light of the image-modulated light R, theP-polarized component is transmitted through the polarized lightseparating surface 66 a of the second polarized beam splitter 66 andtravels toward the second color selective phase plate 67 as theprojected light.

Also, the light B incident on the reflection type liquid crystal displayelement 61B for the light B is image-modulated and reflected. Of thereflected light of the image-modulated light B, the P-polarizedcomponent is again transmitted through the polarized light separatingsurface 66 a of the second polarized beam splitter 66 and is returned tothe light source 1 side, and is removed from the projected light.

On the other hand, of the reflected light of the image-modulated lightB, the S-polarized component is reflected by the polarized lightseparating surface 66 a of the second polarized beam splitter 66 andtravels toward the color selective phase plate 67 as the projectedlight.

At this time, by adjusting the slow axes of the quarter wavelengthplates 62R and 62B provided between the second polarized beam splitter66 and the reflection type liquid crystal display elements 61R and 61Bfor the light R and the light B, respectively, it is possible to effectthe adjustment of the display of the black of the light R and the lightB as in the case of the light G.

Of the projected light of the light R and the light B thus combined intoa light beam, and having emerged from the second polarized beam splitter66, the light R has its polarization direction rotated by 90 degrees bythe second color selective phase plate 67 and becomes an S-polarizedcomponent, and is further analyzed by the emergence side polarizingplate 68 and is incident on the third polarized beam splitter 69.

Also, the light B is intactly transmitted through the second colorselective phase plate 67 as the S-polarized light, and is furtheranalyzed by the emergence side polarizing plate 68 and is incident onthe third polarized beam splitter 69. By being analyzed by the emergenceside polarizing plate 68, the projected light of the light R and thelight B become lights having had its ineffective component cut, wherethe ineffective component is generated by passing through the secondpolarized beam splitter 66, the reflection type liquid crystal displayelements 61R and 61B and the quarter wavelength plates 62R and 62B forrespectively the light R and the light B.

Then, the projected light of the light R and the light B incident on thethird polarized beam splitter 69 is reflected by the polarized lightseparating surface 69 a of the third polarized beam splitter 69, and iscombined with the light G transmitted through the aforementionedpolarized light separating surface 69 a and comes to the projection lens70.

Then, the projected light of the combined light R, light G and light Bis enlarged and projected onto a projection surface such as a screen bythe projection lens 70.

The above-described optical paths are those in a case where thereflection type liquid crystal display element effects white display andtherefore, description will hereinafter be made of optical paths in acase where the reflection type liquid crystal display element effectsblack display.

The optical path of the light G will first be described.

The S-polarized light of the light G transmitted through the dichroicmirror 58 is incident on the incidence side polarizing plate 59, andthereafter is incident on the first polarized beam splitter 60, isreflected by the polarized light separating surface 60 a and comes tothe reflection type liquid crystal display element 61G for the light G.However, the reflection type liquid crystal display element 61G effectsblack display and therefore, the light G is reflected while remainingnot image-modulated.

Accordingly, the light G is still the S-polarized light after reflectedby the reflection type liquid crystal display element 61G and therefore,is again reflected by the polarized light separating surface 60 a of thefirst polarized beam splitter 60, is transmitted through the incidenceside polarizing plate 59 and is returned to the light source 1 side, andis removed from the projected light.

Description will now be made of the optical paths of the light R and thelight B.

The S-polarized lights of the light R and the light B reflected by thedichroic mirror 58 are incident on the incidence side polarizing plate64. Then, the light R and the light B emerge from the incidence sidepolarizing plate 64, and thereafter are incident on the first colorselective phase difference plate 65. The first color selective phasedifference plate 55 has the action of rotating the polarizationdirection of only the light B by 90 degrees, whereby the light B and thelight R are incident on the second polarized beam splitter 66 asP-polarized light and S-polarized light, respectively.

The light R incident on the second polarized beam splitter 66 as theS-polarized light is reflected by the polarized light separating surface66 a of the second polarized beam splitter 66, and comes to thereflection type liquid crystal display element 61R for the light R.Also, the light B incident on the second polarized beam splitter 66 asthe P-polarized light is transmitted through the polarized lightseparating surface 66 a of the second polarized beam splitter 66 andcomes to the reflection type liquid crystal display element 61B for thelight B.

Here, the reflection type liquid crystal display element 61R for thelight R effects black display and therefore, the light R incident on thereflection type liquid crystal display element 61R for the light R isreflected while remaining not image-modulated. Accordingly, the light Ris the S-polarized light still after reflected by the reflection typeliquid crystal display element 61R for the light R and therefore, isagain reflected by the polarized light separating surface 66 a of thesecond polarized beam splitter 66, passes through the incidence sidepolarizing plate 64 and is returned to the light source 1 side, and isremoved from the projected light and thus, becomes black display.

On the other hand, the light B incident on the reflection type liquidcrystal display element 61B for the light B is reflected while remainingnot image-modulated because the reflection type liquid crystal displayelement 61B for the light B effects black display. Accordingly, thelight B is the P-polarized light still after reflected by the reflectiontype liquid crystal display element 61B for the light B and therefore,is again transmitted through the polarized light separating surface 66 aof the second polarized beam splitter 66, is converted into S-polarizedlight by the first color selective phase difference plate 65, istransmitted through the incidence side polarizing plate 64, is returnedto the light source 1 side and is removed from the projected light.

Here, it is desirable in the characteristic of the polarized beamsplitter that the refractive index of the glass material of theaforementioned first, second and third polarized beam splitters be 1.60or greater and 1.90 or less (refractive index for light of a wavelength587.56 nm). The projection lenses (zoom lenses) according to theabove-described Embodiments 1 to 5 will be more preferable if applied toa projection type image display apparatus (particularly a reflectiontype liquid crystal display apparatus using a reflection type liquidcrystal panel) which effects color combination (the combination of theoptical paths of lights in different wavelength areas) by such apolarized beam splitter (an optical element having such a characteristicas reflects light in a predetermined polarization direction in lights inat least a predetermined wavelength area, preferably lights in the red,green and blue areas, and transmits light in a polarization directionorthogonal to the polarization direction thereof.

The foregoing is the optical construction in the projection type imagedisplay apparatus using a reflection type liquid crystal display element(reflection type liquid crystal panel).

A similar effect will be obtained even if a transmission type liquidcrystal display element is used instead of the reflection type liquidcrystal display element.

FIG. 12 is a schematic view of the essential portions of an embodimentof the image projection apparatus of the present invention.

FIG. 12 shows an image projection apparatus in which the aforementionedzoom lens is applied to a tri-panel type color liquid crystal projector,and the image information of a plurality of color lights based on aplurality of liquid crystal display elements is combined through colorcombining means and is enlarged and projected onto a screen surface by aprojection lens.

In FIG. 12, a color liquid crystal projector 101 combines red, green andblue color lights from three R, G and B liquid crystal panels 105R, 105Gand 105B into an optical path by a prism 102 as color combining means,and projects them onto a screen 104 by the use of a projection lens 103comprising the aforementioned zoom lens.

Numerical Embodiments 1 to 3 corresponding to the zoom lenses accordingto Embodiments 1 to 3 will be shown below. In each numerical embodiment,i represents the order of optical surfaces from the enlargement side(front side), Ri represents the radius of curvature of the i-th opticalsurface (the i-th surface), di represents the interval between the i-thsurface and the (i+1)th surface, and ni and vi represent the refractiveindex and the Abbe number, respectively, of the material of the i-thoptical member with d-line as the standard. f represents the focallength.

Also, two surfaces on the rearmost side of Numerical Embodiments 1 to 3are surfaces constituting a glass block GB.

Also, an aspherical shape is represented by

x=(h2/R)/[1+[1−(1+k)(h/R)2]1/2]+Ah4+Bh6+Ch8+DH10+Eh12,

where k represents a conic constant, and A, B, C, D and E representspherical surface coefficients, x represents the displacement in thedirection of the optical axis at the position of a height h from theoptical axis with the surface vertex as the reference, and R representsthe paraxial radius of curvature.

Note that the indication of “e-Z” means “10-Z”.

The relations among the aforementioned Conditional Expressions 1 to 2and the numerical values in Numerical Embodiments 1 to 3 are shown inTable 1 below.

Numerical Embodiment 1 (A) Lens Data Radius of Surface Refractive Abbenumber Surface No. curvature R interval index nd νd 1 40.00375 2.001.746398 27.8 2 20.08345 7.11 3 84.78046 2.50 1.531987 55.8 4 26.8362712.17 5 −23.27356 1.65 1.488976 70.2 6 −101.45165 d6 7 −168.29559 4.501.753999 35.3 8 −37.25336 d8 9 42.90310 3.85 1.753999 35.3 10 252.62854d10 11 64.85383 3.80 1.775817 49.6 12 −64.85383 1.30 1.854159 23.8 132109.01157 14 Stop 15 −20.24525 1.15 1.746398 27.8 16 88.78303 d16 1756.01143 8.60 1.488976 70.2 18 −23.65127 0.50 19 −182.59351 3.551.531987 55.8 20 −50.51247 d20 21 48.32359 6.35 1.488976 70.2 22−78.90134 1.73 23 ∞ 29.20 1.518052 64.1 24 ∞ 9.1042 image planeAspherical Surface Coefficient Surface No. k A B C D E  3 0  2.03893e−5−6.28981e−8 2.15774e−10 −2.68827e−13 7.52135e−17  4 0  9.2681e−6−7.92267e−8 1.70009e−10  3.77076e−14 −9.28005e−16  19 0 −1.74477e−5−2.15534e−8 −2.18198e−11   1.3202e−13 9.24183e−16 20 0 −7.76948e−6−1.76136e−8 3.25435e−11 −7.54099e−14 1.10428e−15 (B) Movement Amountduring Zooming f = 20.54 f = 25.47 f = 32.05 (wide angle) ← →(telephoto) d8 14.00949 5.70622 1.22241 d10 14.45606 9.48876 0.70000 d1412.90960 18.33358 23.89794 d16 2.08219 1.85866 0.70000 d20 0.705368.77547 17.64233 (C) Movement Amount during Focusing object distance = ∞object distance = 7.2 m object distance = 1.7 m object distance = 1.0 md6 0.83134 0.87340 1.00731 1.12726

Numerical Embodiment 2 (A) Lens Data refractive index Abbe numbersurface No. radius of curvature R surface interval d nd νd 1 37.509192.30 1.746398 27.8 2 20.37389 7.11 3 77.78855 2.50 1.531987 55.8 425.91731 12.81 5 −23.44651 1.65 1.488976 70.2 6 −125.97711 d6 7−137.07615 4.78 1.753999 35.3 8 −37.54786 d8 9 42.84232 3.94 1.75399935.3 10 253.00296 d10 11 61.97277 3.94 1.775817 49.6 12 −61.97277 1.301.854159 23.8 13 −769.98320 9.03 14 stop d14 15 −20.24381 1.15 1.74639827.8 16 90.95572 d16 17 59.99538 8.73 1.488976 70.2 18 −22.65899 d18 19−192.36222 3.11 1.531987 55.8 20 −61.14919 d20 21 47.53963 6.61 1.48897670.2 22 −73.61163 1.73 23 ∞ 29.20 1.518052 64.1 24 ∞ 9.0925 image planeAspherical Surface Coefficient surface No. k A B C D E  3 0  2.28124e−5−7.72020e−8 2.85372e−10 −4.53387e−13 3.05335e−16  4 0.468172  9.02544e−6−9.78557e−8 2.10056e−10 −3.42224e−14 −8.15677e−16  19 0 −2.16700e−5−4.51762e−8 6.62042e−12 −1.35685e−13 1.35733e−15 20 8.57459 −6.94481e−6−3.15546e−8 7.68963e−11 −2.39733e−13 1.43474e−15 (B) Movement Amountduring Zooming f = 20.55 f = 25.40 f = 32.05 (wide angle) ← →(telephoto) d8 11.45649 4.34484 1.15096 d10 15.98133 10.36014 0.81918d14 11.55478 16.97503 21.67997 d16 2.71490 2.33827 0.70000 d18 0.500000.89124 2.17917 d20 0.70000 7.99798 16.37823 (C) Movement Amount duringFocusing object distance = ∞ object distance = 7.2 m object distance =1.7 m object distance = 1.0 m D6 0.95738 1.00144 1.14156 1.26685

Numerical Embodiment 3 (A) Lens Data Radius of Surface Refractive Abbenumber Surface No. curvature R interval d index nd νd 1 40.00000 2.001.746398 27.8 2 20.84646 6.48 3 79.11466 2.50 1.531987 55.8 4 27.4918411.88 5 −24.51906 1.65 1.488976 70.2 6 −159.56948 d6 7 −217.26019 4.271.753999 35.3 8 −39.16574 d8 9 41.46397 3.46 1.753999 35.3 10 173.59183d10 11 68.77912 3.78 1.775817 49.6 12 −68.77912 1.30 1.854159 23.8 13−370.86456 8.29 14 stop d14 15 −20.61697 1.15 1.746398 27.8 16 75.848882.61 17 51.47248 8.84 1.498306 81.5 18 −24.57231 0.99 19 −154.65491 3.941.531987 55.8 20 −48.21169 d20 21 49.63966 5.97 1.488976 70.2 22−97.49254 1.73 23 ∞ 29.20 1.518052 64.1 24 ∞ 9.11249 image planeAspherical Surface Coefficient surface No. k A B C D E  3 0  2.39002e−5−7.85335e−8 2.82840e−10 −5.10385e−13 4.82670e−16  4 0.82000  9.67314e−6−9.28713e−8 1.78722e−10 −1.30937e−13 −4.76430e−16  19 0 −1.84241e−5−2.52060e−8 1.57386e−11 −5.29428e−14 8.63637e−16 20 4.58709 −2.79208e−6−1.71898e−8 1.27531e−10 −3.76035e−13 1.37862e−15 (B) Movement Amountduring Zooming f = 20.55 f = 25.40 f = 32.05 (wide angle) ← →(telephoto) d8 18.54472 7.91422 1.08868 d10 11.02830 7.76763 0.70000 d1412.62326 16.80830 21.91464 d20 0.70000 10.40612 19.19295 (C) MovementAmount during Focusing object object distance = ∞ distance = 7.2 mobject distance = 1.7 m object distance = 1.0 m D6 0.80742 0.853470.99998 1.13112

TABLE 1 Conditional Embodiment Expressions 1 2 3 (1) νdR-νdF 42.4 42.442.4 $(2)\mspace{11mu} \frac{DP}{fw}$ 8.0 7.7 8.5

According to the present embodiment described above, there is obtained azoom lens suitable, for example, for use in a liquid crystal projectorwhich achieves the downsizing of an entire lens system, and yet whichwell corrects various aberrations resulting from focusing, and has goodoptical performance over the whole of a projection distance.

1. A zoom lens comprising: a plurality of lens units including a firstlens unit which doesn't move for zooming, is disposed most adjacent toan enlargement side and has negative refractive power, wherein at leastone of said plurality of lens units is moved in the direction of theoptical axis thereof during zooming; and wherein said first lens unitincludes, in succession from enlargement side, a 1-1st lens unitcomprising at least one lens having negative refractive power and movedduring focusing; and a 1-2nd lens unit having positive refractive powerand fixed during focusing.
 2. A zoom lens according to claim 1, whereinsaid 1-1st lens unit comprises a plurality of negative lenses.
 3. A zoomlens according to claim 1, wherein said 1-1st lens unit is disposed moreadjacent to the enlargement side than 1-2nd lens unit.
 4. An imageprojection apparatus comprising: a zoom lens according to claim 1; adisplay unit for forming an original picture; wherein the originalpicture formed by the display unit is projected onto a projectionsurface by the zoom lens.
 5. A zoom lens comprising: a first lens unitwhich is disposed most adjacent to an enlargement side, has negativerefractive power, and doesn't move for zooming, a last lens unitdisposed most adjacent to a reduction side and having positiverefractive power; and one or more lens units moved in the direction ofthe optical axis thereof during zooming; wherein a first lens in saidfirst lens unit, which is disposed most adjacent to the enlargement sidewithin said first lens unit, has negative refractive power, the lastlens in said last lens unit, which is disposed most adjacent to thereduction side within said last lens unit, has positive refractivepower, and the following condition is satisfied,32<νdR−νdF, where νdF represents the Abbe number of the material of thefirst lens and νdR represents the Abbe number of the material of thelast lens.
 6. An image projection apparatus comprising: a zoom lensaccording to claim 5; and a display unit for forming an originalpicture; wherein the original picture formed by the display unit isprojected onto a projection surface by the zoom lens.